Which of the following numbers is a factor of 90? ${4,6,11,12,13}$
Answer: By definition, a factor of a number will divide evenly into that number. We can start by dividing $90$ by each of our answer choices. $90 \div 4 = 22\text{ R }2$ $90 \div 6 = 15$ $90 \div 11 = 8\text{ R }2$ $90 \div 12 = 7\text{ R }6$ $90 \div 13 = 6\text{ R }12$ The only answer choice that divides into $90$ with no remainder is $6$ $ 15$ $6$ $90$ We can check our answer by looking at the prime factorization of both numbers. Notice that the prime factors of $6$ are contained within the prime factors of $90$ $90 = 2\times3\times3\times5 6 = 2\times3$ Therefore the only factor of $90$ out of our choices is $6$. We can say that $90$ is divisible by $6$.